/Engine/Source/Runtime/Core/Public/Containers/SparseArray.h
Constructs a new item at the lowest free index of the array. This requires a search which can be accelerated with LowestFreeIndexSearchStart.Indexto the new item
template<typename... ArgsType> int32 EmplaceAtLowestFreeIndex ( int32 & LowestFreeIndexSearchStart, ArgsType &&... Args )